fix get aws voice should not be limit in en-US

lib/get-tts-voices.js

@@ -97,7 +97,7 @@ const getAwsVoices = async(_client, logger, credentials) => {
         secretAccessKey
       }
     });
-    const command = new DescribeVoicesCommand({LanguageCode: 'en-US'});
+    const command = new DescribeVoicesCommand({});
     const response = await client.send(command);
     return response;
   } catch (err) {